Field of the Invention
The invention relates generally to downhole electric equipment, and more particularly to systems and methods for improving the reliability and ease of installation of electrical connections between power cables and downhole electric equipment such as electric submersible pumps (ESP's).
Related Art
Electric submersible pump (ESP) systems are commonly positioned within subterranean wells and used to pump fluids from the wells. Power suitable to drive the ESP systems is produced at the surface of the wells and is delivered to the ESP systems via power cables that extend into the wells. The power cables are typically spliced to motor lead extensions (heavy gauge conductive wires), which are in turn connected to the motor of the ESP using a “pothead” connector.
Conventionally, a motor lead extension extends along the exterior of the ESP from near the top of the ESP to the motor. At the top of the motor, the motor lead extension is curved inward so that the pothead connector at the end of the motor lead extension can be coupled to the motor head. The motor head is normally configured to accept the pothead connector at an angle with respect to the axis of the system in order to facilitate the connection of the pothead to the motor head. The connection is angled to accommodate the position of the pothead as the stiff motor lead extension is curved inward toward the connection on the motor head.
Although the angled connection of the pothead to the motor head relieves the problem of the motor lead extension affecting the orientation of the pothead, it can cause several other problems. For instance, the motor lead extension and pothead have some weight and therefore tend to hang straight down. Consequently, it is necessary for the installer to manually reorient the pothead to the angle of the motor head interface. As noted above, the motor lead extension is very stiff, and it may be difficult to accurately position the pothead to correctly engage the motor head.
Another, related problem is that, because the pothead connector is angled with respect to the axis of the motor, the connector extends outward, radially, beyond the outer diameter of the motor and into the annulus between the motor and the casing of the well. Further, the motor lead extension, which is aligned with the pothead connector, also extends outward beyond the outer diameter of the motor and into the annulus between the motor and the casing. As a result of the pothead and the motor lead extension extending beyond the outer diameter of the motor, the equipment designer must either reduce the size of the motor to accommodate this, or risk of damage to the pothead or motor lead extension when the motor is installed in the narrow annulus in the well.
Yet another problem is that the connection between the pothead and the motor head may be damaged in the process of trying to align and secure these components. More specifically, the insulation block (“i-block”) that is positioned in the motor head to provide insulation between the conductors at the pothead interface may be very brittle, and an attempt to secure a misaligned pothead to the motor may crack the i-block. The i-block may then fail to provide the necessary electrical isolation of the conductors, which can result in shorting of the conductors and failure of the motor.
Another problem with conventional pothead connectors is that the interface between the connector and the motor housing provides only a small area for sealing. Typically, a relatively small, annular seal is positioned around a portion of the pothead connector that plugs into the motor housing. Also, conventional pothead connectors are typically secured to the motor housing by a pair of bolts on opposite sides of the plug-in portion of the connector. As the pothead connector becomes more slender and as the spacing of the bolts increases, the deflection of the connector housing increases, resulting in reduced contact pressure on the sealing surface of the connector. The use of only two bolts in the conventional design may also require increasingly large bolts to provide the desired preload, but the amount of space for these bolts is decreasing as motor diameters are reduced.